Oil Sands occur widely and are loosely defined as being naturally occurring oil deposits, which generally comprise a mineral matrix impregnated with extra-heavy oil—bitumen, tar or asphalt—and, depending upon their location, vary widely in mineral and oil composition. While oil sands are found in many regions of the world, the largest deposits occur in Western Canada and in Venezuela. In the United States, oil sands are primarily concentrated in Eastern Utah.
Where oil sand deposits occur close to the surface, recovery is achieved by mining the deposit and extracting the oil in a water-washing process. In deposits too deep to mine, steam is pumped into the deposit to wash the oil from the sand in-situ and recovered oil is pumped to the surface. In either case, recovered oil must be upgraded before it can be processed in a conventional refinery. Some Canadian productions are processed in Upgrading Plants, yielding high quality synthetic crude which is sold to refineries in the United States and Canada; the remaining production is shipped as a diluted bitumen stream to specially designed refineries, mainly in the United States.
The mineral matrix in the Canadian oil sands is mainly loosely consolidated, water-wet sand. Oil is readily released from the matrix by forming slurry with hot water and then allowing separated oil to float to the surface as “froth” in a cone shaped separation vessel. This process, typically referred to as a warm-water extraction process, provides recovered oil (bitumen froth) containing approximately 10% mineral matter and up to 30% water. Further processing is typically required to produce clean oil. In this process a solvent is added and the mineral matter and water are removed by a combination of settling or mechanical devices, such as high-speed centrifuges.
The two-step process has overall recovery efficiency greater than 90% and is practiced on a colossal scale. A typical processing plant will produce about 150,000 barrels per day. The main advantage of warm-water processing is its simplicity. Disadvantages include the high water usage and need for huge containment ponds to store the dispersed clays.
Since the mid 1930's, when oil sands extraction experimentation began, a number of alternative extraction processes were developed in Canada and the United States. Most are variations on the warm-water process.
In a typical solvent extraction method, following the crushing and removal of oversize material (rocks), oil sands are contacted with a solvent, usually in a rotating drum. In this process the oil is dissolved by the solvent which frees it from the mineral matrix. The oil/solvent mixture is then drained from the mineral and the mineral is again washed with a new portion of the solvent. The mineral, now free of oil but saturated with solvent, is stripped to recover the solvent for recycling.
U.S. Pat. No. 4,719,008 to Sparks et al and U.S. Pat. No. 4,057,486 to Meadows et al, each herein incorporated by reference, disclose a solvent extraction process of oil from oil sands involving a continuous combined extraction-agglomeration step employing an organic solvent. While the main advantage of the solvent route is the ability to process all grades of oil sand with high (95%) recovery efficiency, the high energy required for recovery of solvent from the washed mineral and the need for sealed equipment to contain solvent losses make the solvent extraction processes costly and complex.
U.S. Pat. Nos. 4,167,470 and 4,239,617 to Karnofsky et al, disclose a solvent extraction process of oil from oil bearing diatomite ore, wherein the ore is extracted by countercurrent decantation with a hydrocarbon solvent which is later recovered from the extractor by repeated evaporations and stripping. Water is employed to displace a major portion of the solvent therefrom, which may then be recovered.
U.S. Pat. No. 4,160,718 to Rendall discloses a continuous solvent extraction process of oil from oil sands employing a closed rotary contactor.
Unlike the solvent extraction methods, in the thermal extraction methods following the crushing and removal of oversize, the oil sands are rapidly heated to a high temperature (typically over 500° C.) in a containment vessel. The high temperature cracks the heavy oil forming lighter oil, gas and coke, with the lighter oil and gas being removed as vapors and the coke remaining as a coating on the mineral sand. Next, the coke-coated sand is burned in a separate vessel and the hot sand is returned to the coking vessel to mix with incoming oil sand and provide heat for the coking process. As with other methods, the sand is quenched with water and discarded, and the light oil is condensed to form a partially upgraded product.
The main advantage of the thermal processing is that it combines oil extraction with partial upgrading. Instead of extra-heavy oil, the product is higher API (American Petroleum Institute measure of relative density) oil which would be more commercially valuable. As with the solvent extraction methods, however, the main disadvantages of thermal processing are their complexity and high cost.